By the structure of a silica is meant its properties which describe the degree and extent of the assembly of its primary particles into secondary particles or to tertiary aggregates. According to the facts available today, which concern the characterization of the structure of furnace blacks, by the use of the Brabender absorption number according to Cabot when applied to precipitated silicas, there can be shown a clear connection between the so-called dibutylphthalate absorption number (DBP number in ml/g or %) and the structure properties (see German Pat. No. 1767332, col. 2, lines 45-64, and related Turk U.S. Pat. No. 4,001,379. The entire disclosure of the Turk U.S. patent is hereby incorporated by reference and relied upon).
As the state of the art, there are known types of silica which in regard to their structure differentiate from the normal silicas (reinforcing materials for rubber) having average structural dimensions.
Thereby, it is a matter of precipitated silicas or silica gels in which products are formed through particular variants of the drying process whose structure is regarded as increased. The aerogels (Ullmanns Enzyklopadie der technischen Chemie, 3rd edition, Vol. 15, page 725 (1949)) which are obtained by supercritical dewatering of silica organo-hydrogels (Kistler U.S. Pat. No. 2,249,767), or by jet mill drying of silica hydrogels (German Pat. No. 1036220) belong to this class. Furthermore, there are included in this group those silicas and silica gels whose intermicellar liquid before the drying step consists of organic solvents or mixtures of such solvents with water (Marshall U.S. Pat. No. 2,285,449, German AS No. 1008717, German Pat. No. 1089736). Also included are spray dried silicas (Netherlands published application No. 65 02791, German Pat. No. 2447613) and finally the precipitated silicas obtained by shearing (German patent application No. F 14059 VI c/12i, German AS No. 1000793, German Pat. No. 1767332, and the related Turk U.S. Pat. No. 4,001,379).
The following compilation (Table 1) contains a comparative summary concerning the state of the art in the comparison to the "normal" precipitated silica with average structure. There are added to the summary additionally the data of three different silicas according to the invention. The comparison of the numbered materials leads to the statement that the invention surprisingly has succeeded in producing highly structured silicas and silica gels with a surface area of more than 400 m.sup.2 /g in combination with a DBP number of more than 300 percent.